Methanol is produced by contacting a synthesis gas containing at (east carbon monoxide, carbon dioxide and hydrogen with a catalyst. This synthesis gas is converted to methanol in a separate vessel.
DME can be produced either by direct processes or indirect (two step) processes.
The direct processes convert synthesis gas to methanol and then methanol to DME in the same converter.
The two step processes include the conventional two step process in which methanol is dehydrated in a catalytic fixed bed vessel and the vessel effluents are cooled and distilled to produce DME and methanol which is recycled to the converter.
The Lurgi Mega DME process uses natural gas to produce methanol which is then treated in a vessel to produce a mixture of DME, water and other hydrocarbons. The mixture is then distilled.
The Haldor Topsoe DME process converts synthesis gas to methanol and then converts the methanol to DME in a fixed bed vessel.
Most of these processes use an air separation unit (ASU) to produce oxygen at high pressure to convert natural gas to synthesis gas, the synthesis gas either being sent to a single converter where it is converted to methanol and then to DME in a direct process or being sent to a first converter to be converted to methanol, the methanol then being removed and converted to DME in a two step process.
As described in U.S. Pat. No. 6117916, an ASU produces oxygen at 40 bar and the oxygen reacts with steam and natural gas in a partial oxidation reactor to produce synthesis gas. The synthesis gas at 40 bar is then compressed to 70 bar and is sent to a methanol reactor, thereby producing methanol at 66 bar.
Usually two synthesis gas compressors in parallel are used to avoid maintenance problems. These compressors are costly both in capital investment and in terms of upkeep.